Issue

Choosing the Right Sorbent for Electronics Applications

11/01/2006

BY ROBERT SABDO, Multisorb Technologies

Maintaining the stability of moisture-sensitive electronic components and assemblies is a fundamental concern of manufacturers. Without adequate moisture management, moisture ingress results in oxidation and other product breakdown to severely impact the quality, safety, and longevity of sensitive products.

Sorbents adsorb moisture, oxygen, odors, hydrocarbons, and other volatiles from constrained environments. When incorporated early in the design process, they can prevent moisture and oxidation problems and help protect components and subsystems. Solutions can be as simple as a drop-in sachet or a tightly integrated part of the structure.

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Ingress of moisture, in the presence of oxygen, creates the perfect environment for oxidation, causing salt build-up, dendritic growth, or tin whiskers. The resulting corrosion often leads to high production scrap or field failures. A key decision in the development of any sorbent strategy is to determine how to combat oxidation. Eliminating oxygen directly is often technically difficult and expensive. An alternative is to develop a strategy to manage moisture, the mediating factor to the oxidation reaction. Desiccants are the most common solution.

Some key factors to consider when choosing a desiccant are total capacity for moisture and moisture aggressiveness. The adsorption capacity and the adsorption rate of five common desiccants are shown in Figures 1 and 2. These include montmorillonite clay, silica gel, molecular sieve (synthetic zeolite), calcium sulfate, and calcium oxide.

These desiccants are prescribed depending on the type of technology or design priority. Applications such as LEDs, optical sensors, electronic circuitry, and semiconductors incorporate different desiccant formats due to varying sorbent requirements.

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Calcium oxide is a frequent choice for sensitive LED components because it removes minute amounts of moisture even at low relative humidity. Yet its exothermic properties can create potential problems in temperature-sensitive electronics applications. Further, it has a limited adsorption capacity, initially removing large amounts of water, but tapering off over time, thereby reducing the longevity of moisture protection. Adsorption selectivity is also an issue to be considered: calcium oxide adsorbs many substances in the environment, whereas other sorbents - molecular sieves for example - are chemically formulated to target only water.

By contrast, optical sensors and components are known for their extreme sensitivity to moisture that accumulates over time. Moisture molecules cause undesirable reflections and reduce the effectiveness of light beams emitted from lasers. Maintaining long-term desiccation in vacuum-sealed compartments of light-emitting devices can be crucial to ensuring functionality over time.

In the case of microchips and semiconductors, if moisture is not managed from the outset, heat during manufacturing may cause accumulated moisture to expand and explode the component. Microchips and semiconductors will then have to be reconditioned, which is both expensive and labor-intensive. Popcorning, which occurs when accumulated moisture in hermetically-sealed electronic components cannot escape, can also lead to delamination of the die/package interface and to plastic package cracking.

One solution to the oxidation threat, especially when dealing with hermetically sealed components, is to build the sorbent into the device itself and protect it on a piece-by-piece basis. Specially-engineered sorbents can be incorporated into the material of the manufactured product, serving as structural components while also providing protection from moisture and oxidation.

Sorbent technology offers a diverse array of options that can be customized to fit a variety of design and manufacturing parameters. Key to ensuring product stability and integrity of electronics is the incorporation of a structural desiccant during the initial design phase.